Process and apparatus for producing diesel

ABSTRACT

A process and apparatus are disclosed for hydrocracking hydrocarbon feed in a hydrocracking unit and hydrotreating a diesel product from the hydrocracking unit in a hydrotreating unit. The hydrocracking unit and the hydrotreating unit share the same recycle gas compressor. A make-up hydrogen stream may also be compressed in the recycle gas compressor. A warm separator separates recycle gas and hydrocarbons from diesel in the hydrotreating effluent, so fraction of the diesel is relatively simple. The warm separator also keeps the diesel product separate from the more sulfurous diesel in the hydrocracking effluent, and still retains heat needed for fractionation of lighter components from the low sulfur diesel product.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Provisional Application No.61/549,978 filed Oct. 21, 2011, the contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The field of the invention is the production of diesel by hydrocracking.

BACKGROUND OF THE INVENTION

Hydrocracking refers to a process in which hydrocarbons crack in thepresence of hydrogen and catalyst to lower molecular weighthydrocarbons. Depending on the desired output, the hydrocracking zonemay contain one or more beds of the same or different catalyst.

Hydrocracking is a process used to crack hydrocarbon feeds such asvacuum gas oil (VGO) to diesel including kerosene and gasoline motorfuels.

Mild hydrocracking is generally used upstream of a fluid catalyticcracking (FCC) or other process unit to improve the quality of anunconverted oil that can be fed to the downstream unit, while convertingpart of the feed to lighter products such as diesel. As world demand fordiesel motor fuel is growing relative to gasoline motor fuel, mildhydrocracking is being considered for biasing the product slate in favorof diesel at the expense of gasoline. Mild hydrocracking may be operatedwith less severity than partial or full conversion hydrocracking tobalance production of diesel with the FCC unit, which primarily is usedto make naphtha. Partial or full conversion hydrocracking is used toproduce diesel with less yield of the unconverted oil which can be fedto a downstream unit.

Due to environmental concerns and newly enacted rules and regulations,saleable diesel must meet lower and lower limits on contaminates, suchas sulfur and nitrogen. New regulations require essentially completeremoval of sulfur from diesel. For example, the ultra low sulfur diesel(ULSD) requirement is typically less than about 10 wppm sulfur.

There is a continuing need, therefore, for improved methods of producingmore diesel from hydrocarbon feedstocks than gasoline. Such methods mustensure that the diesel product meets increasingly stringent productrequirements.

BRIEF SUMMARY OF THE INVENTION

In a process embodiment, the invention comprises a process for producingdiesel from a hydrocarbon stream comprising compressing a make-uphydrogen stream in a compressor to provide a compressed make-up hydrogenstream. The compressed make-up hydrogen stream is further compressed ina recycle gas compressor to provide a compressed hydrogen stream. Ahydrocracking hydrogen stream is taken from the compressed hydrogenstream. The hydrocarbon stream is hydrocracked in the presence of thehydrocracking hydrogen stream and hydrocracking catalyst to provide ahydrocracking effluent stream. At least a portion of the hydrocrackingeffluent stream is fractionated to provide a diesel stream. The dieselstream is hydrotreated in the presence of a hydrotreating hydrogenstream and hydrotreating catalyst to provide a hydrotreating effluentstream.

In an additional process embodiment, the invention further comprises aprocess for producing diesel from a hydrocarbon stream comprisingcompressing a make-up hydrogen stream in a compressor to provide acompressed make-up hydrogen stream. The hydrocarbon stream ishydrocracked in the presence of a hydrocracking hydrogen stream andhydrocracking catalyst to provide a hydrocracking effluent stream. Thehydrocracking effluent stream is separated into a vaporous hydrocrackingeffluent stream comprising hydrogen and a liquid hydrocracking effluentstream. The vaporous hydrocracking effluent stream and the compressedmake-up hydrogen stream are compressed to provide a compressed hydrogenstream. The hydrocracking hydrogen stream and a hydrotreating hydrogenstream are taken from the compressed hydrogen stream. The liquidhydrocracking effluent stream is fractionated to provide a dieselstream. The diesel stream is hydrotreated in the presence of thehydrotreating hydrogen stream and a hydrotreating catalyst to provide ahydrotreating effluent stream.

In an alternative additional process embodiment, the invention furthercomprises a process for producing diesel from a hydrocarbon streamcomprising compressing a make-up hydrogen stream in a compressor toprovide a compressed make-up hydrogen stream. The compressed make-uphydrogen stream is compressed in a recycle gas compressor to provide acompressed hydrogen stream. A hydrocracking hydrogen stream is takenfrom the compressed hydrogen stream. The hydrocarbon stream ishydrocracked in the presence of the hydrocracking hydrogen stream andhydrocracking catalyst to provide a hydrocracking effluent stream. Atleast a portion of the hydrocracking effluent stream is fractionated toprovide a diesel stream. The diesel stream is hydrotreated in thepresence of a hydrotreating hydrogen stream and hydrotreating catalystto provide a hydrotreating effluent stream. Lastly, at least a portionof the hydrotreating effluent stream comprising hydrogen is mixed withat least a portion of the hydrocracking effluent stream.

In an apparatus embodiment, the invention further comprises an apparatusfor producing diesel comprising a hydrocracking reactor in communicationwith a compressor on a make-up hydrogen line and a hydrocarbon feed linefor hydrocracking the hydrocarbon stream to lower boiling hydrocarbons.A recycle gas compressor is in communication with the hydrocrackingreactor and the make-up hydrogen line for compressing a vaporoushydrocracking effluent stream comprising hydrogen and a compressedmake-up hydrogen stream to provide a compressed hydrogen stream in acompressed hydrogen line. Lastly, a hydrotreating reactor is incommunication with the compressed hydrogen line and the hydrocrackingreactor for hydrotreating a diesel stream to produce low sulfur diesel.

In an alternative apparatus embodiment, the invention further comprisesan apparatus for producing diesel comprising a make-up hydrogen line.One or more compressors is in communication with the make-up hydrogenline for compressing the make-up hydrogen stream. A hydrocarbon feedline is for carrying a hydrocarbon stream. A hydrocracking reactor is incommunication with the make-up hydrogen line and the hydrocarbon feedline for hydrocracking the hydrocarbon stream to lower boilinghydrocarbons. A recycle gas compressor is in communication with thehydrocracking reactor and the one or more compressors for compressing avaporous hydrocracking effluent stream comprising hydrogen and acompressed make-up hydrogen stream to provide a compressed hydrogenstream in a compressed hydrogen line. A fractionation section is incommunication with the hydrocracking reactor for fractionating a liquidhydrocracking effluent stream to produce a diesel stream carried in adiesel line. Lastly, a hydrotreating reactor is in communication withthe compressed hydrogen line and the diesel line for hydrotreating thediesel stream to produce low sulfur diesel.

In a further apparatus embodiment, the invention further comprises anapparatus for producing diesel comprising a hydrocracking reactor incommunication with one or more compressors on a make-up hydrogen lineand a hydrocarbon feed line for hydrocracking the hydrocarbon stream tolower boiling hydrocarbons. A recycle gas compressor is in communicationwith the make-up hydrogen line and the hydrocracking reactor forcompressing a vaporous hydrocracking effluent stream comprising hydrogento provide a compressed hydrogen stream in a compressed hydrogen line. Ahydrotreating reactor is in communication with the compressed hydrogenline and the hydrocracking reactor for hydrotreating the diesel streamto produce low sulfur diesel. A warm separator is in communication withthe hydrotreating reactor for separating the hydrotreating effluentstream into a vaporous hydrotreating effluent stream comprising hydrogenin an overhead line and a liquid hydrotreating effluent stream in abottoms line. Lastly, the recycle gas compressor is in communicationwith the overhead line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified process flow diagram of an embodiment of thepresent invention.

FIG. 2 is a simplified process flow diagram of an alternative embodimentof the present invention.

DEFINITIONS

The term “communication” means that material flow is operativelypermitted between enumerated components.

The term “downstream communication” means that at least a portion ofmaterial flowing to the subject in downstream communication mayoperatively flow from the object with which it communicates.

The term “upstream communication” means that at least a portion of thematerial flowing from the subject in upstream communication mayoperatively flow to the object with which it communicates.

The term “column” means a distillation column or columns for separatingone or more components of different volatilities. Unless otherwiseindicated, each column includes a condenser on an overhead of the columnto condense and reflux a portion of an overhead stream back to the topof the column and a reboiler at a bottom of the column to vaporize andsend a portion of a bottoms stream back to the bottom of the column.Feeds to the columns may be preheated. The top pressure is the pressureof the overhead vapor at the vapor outlet of the column. The bottomtemperature is the liquid bottom outlet temperature. Overhead lines andbottoms lines refer to the net lines from the column downstream of thereflux or reboil to the column.

As used herein, the term “True Boiling Point” (TBP) means a test methodfor determining the boiling point of a material which corresponds toASTM D2892 for the production of a liquefied gas, distillate fractions,and residuum of standardized quality on which analytical data can beobtained, and the determination of yields of the above fractions by bothmass and volume from which a graph of temperature versus mass %distilled is produced using fifteen theoretical plates in a column witha 5:1 reflux ratio.

As used herein, the term “conversion” means conversion of feed tomaterial that boils at or below the diesel boiling range. The cut pointof the diesel boiling range is between about 343° and about 399° C.(650° to 750° F.) using the True Boiling Point distillation method.

As used herein, the term “diesel boiling range” means hydrocarbonsboiling in the range of between about 132° and about 399° C. (270° to750° F.) using the True Boiling Point distillation method.

DETAILED DESCRIPTION

Mild hydrocracking reactors operate at low severity and therefore lowconversion. The diesel produced from mild hydrocracking is not ofsufficient quality to meet applicable fuel specifications particularlywith regard to sulfur. As a result, the diesel produced from mildhydrocracking must be processed in a hydrotreating unit to allowblending into finished diesel. In many cases, it is attractive tointegrate the mild hydrocracking unit and the hydrotreating unit toreduce capital and operating costs.

A typical hydrocracking unit has both a cold separator and a cold flashdrum. It often, but not always, has a hot separator and a hot flashdrum. A typical hydrotreating unit has only a cold separator. The coldseparator may be operated at a lower temperature for obtaining optimalhydrogen separation for use as recycle gas, but this proves thermallyinefficient as the hydrotreated liquid stream must be reheated forfractionation to obtain the low sulfur diesel.

To avoid this cooling and reheating without impacting the hydrogenseparation, a hydrotreating unit is utilized in parallel withhydrocracking unit, a common recycle gas compressor and a coldseparator. The recycle gas splits to each unit after compression.Make-up gas can be added to the recycle gas stream upstream to therecycle gas compressor. Make-up gas may be added upstream of the recyclegas compressor, to utilize the recycle gas compressor for compression ofhydrogen gas fed to the hydrocracking reactor and the hydrotreatingreactor.

The hydrotreating unit may employ a warm separator to extract a warmliquid product and then combine the vaporous hydrotreating effluentphase with the hydrocracking effluent. This arrangement allows thehydrotreating and hydrocracking units to operate at similar pressures.Additionally, the vaporous hydrotreating effluent may be sent to thecold separator to further separate hydrogen from hydrocarbon to providerecycle gas. The liquid hydrotreating effluent from the warm separatordoes not have to be reheated as much before fractionation. Furthermore,the liquid hydrotreating effluent comprises predominantly low sulfurdiesel, so fractionation of the low sulfur diesel is simpler.

The invention involves splitting all make-up gas and recycle gas betweenthe hydrocracking unit and the hydrotreating unit. The make-up gasaddition to the hydrocracking unit is advantageous because the feedstockto the hydrocracking reactor will typically have high coke precursorswhich lead to higher catalyst deactivation rates and shorter catalystlife. Using the make-up gas to increase the hydrogen partial pressure inthe hydrocracking reactor will render the hydrocracking operation moreefficient.

The apparatus and process 8 for producing diesel comprise a compressionsection 10, a hydrocracking unit 12, a hydrotreating unit 14 and afractionation zone 16. Hydrocarbon feed is first fed to thehydrocracking unit 12 and converted to lower boiling hydrocarbonsincluding diesel. The diesel is fractionated in a fractionation sectiontherein and forwarded to the hydrotreating unit 14 to provide lowersulfur diesel.

A make-up hydrogen stream in a make-up hydrogen line 20 is fed to atrain of one or more compressors 22 in the compression section 10 toboost the pressure of the make-up hydrogen stream and provide acompressed make-up stream in line 26. The compressed make-up stream incompressed make-up hydrogen line 26 may join with a vaporoushydrocracking effluent stream comprising hydrogen in an overhead line 42to provide an introductory hydrogen stream in line 28. The compressedmake-up hydrogen stream may be added to the vaporous hydrocrackingeffluent stream upstream of a recycle gas compressor 50 at a locationsuch that, relative to the compressed make-up hydrogen line 26, therecycle gas compressor 50 is upstream of any hydroprocessing reactor,such as a hydrocracking reactor 36 or a hydrotreating reactor 92.Consequently, no hydroprocessing reactor is located intermediate of thecompressed make-up hydrogen line 26 and the recycle gas compressor 50.

The introductory hydrogen stream in line 28 comprising the compressedmake-up hydrogen stream and the vaporous hydrocracking effluent streammay be compressed in a recycle gas compressor 50 to provide a compressedhydrogen stream in a compressed hydrogen line 52 which includescompressed vaporous hydrocracking effluent. The recycle gas compressor50 may be in downstream communication with the hydrocracking reactor 36,the make-up hydrogen line 20 and the one or more compressors 22.

In an embodiment, the compressed make-up hydrogen stream may be added tothe compressed hydrogen line 52 downstream of the recycle gas compressor50. However, the pressure of the compressed hydrogen stream in line 52may be too great to admit the make-up hydrogen stream without addingmore compressors on the make-up hydrogen line 20. Consequently, addingthe compressed make-up hydrogen stream to the vaporous hydrocrackingeffluent stream in line 42 upstream of the recycle gas compressor 50 maybe advantageous, despite the increased duty on the recycle gascompressor 50 due to greater throughput. Adding the compressed make-uphydrogen stream upstream of the recycle gas compressor 50, however, maydiminish the need for an additional compressor 22 on the make-uphydrogen line 20.

The compressed hydrogen stream in line 52 may be split between twohydrogen streams at a split 54. A first hydrocracking hydrogen stream istaken from the compressed hydrogen stream in the compressed hydrogenline 52 at the split 54 in a first hydrogen split line 30. A secondhydrotreating hydrogen stream is taken from the compressed hydrogenstream in the compressed hydrogen line 52 at the split 54 in a secondhydrogen split line 56. The first hydrogen split line 30 is in upstreamcommunication with the hydrocracking reactor 36 and the secondhydrotreating hydrogen stream in a second hydrogen split line 56 is inupstream communication with the hydrotreating reactor 92.

The hydrocracking hydrogen stream in the first hydrogen split line 30taken from the compressed hydrogen stream in line 52 may join ahydrocarbon feed stream in line 32 to provide a hydrocracking feedstream in line 34.

The compressed make-up hydrogen stream in line 26 may also join thecompressed hydrogen stream downstream of a split 54, so the make-uphydrogen will be directed to supplying the hydrogen requirements to thehydrocracking reactor 36 or the hydrotreating reactor 92 not filled bythe recycle hydrogen stream in line 52. If the compressed make-uphydrogen stream in line 26 joins the compressed hydrogen stream upstreamof the split 54, make-up gas is allowed to go to the hydrotreating unit14 as well as to the hydrocracking unit 12.

The hydrocarbon feed stream is introduced in line 32 perhaps through asurge tank. In one aspect, the process and apparatus described hereinare particularly useful for hydroprocessing a hydrocarbonaceousfeedstock. Illustrative hydrocarbon feedstocks include hydrocarbonaceousstreams having components boiling above about 288° C. (550° F.), such asatmospheric gas oils, VGO, deasphalted, vacuum, and atmospheric residua,coker distillates, straight run distillates, solvent-deasphalted oils,pyrolysis-derived oils, high boiling synthetic oils, cycle oils,hydrocracked feeds, cat cracker distillates and the like. Thesehydrocarbonaceous feed stocks may contain from about 0.1 to about 4 wt-%sulfur.

A suitable hydrocarbonaceous feedstock is a VGO or other hydrocarbonfraction having at least about 50 percent by weight, and usually atleast about 75 percent by weight, of its components boiling at atemperature above about 399° C. (750° F.). A typical VGO normally has aboiling point range between about 315° C. (600° F.) and about 565° C.(1050° F.).

Hydrocracking refers to a process in which hydrocarbons crack in thepresence of hydrogen to lower molecular weight hydrocarbons. Ahydrocracking reactor 36 is in downstream communication with the one ormore compressors 22 on the make-up hydrogen line 20 and the hydrocarbonfeed line 32. The hydrocracking feed stream in line 34 may be heatexchanged with a hydrocracking effluent stream in line 38 and furtherheated in a fired heater before entering the hydrocracking reactor 36for hydrocracking the hydrocarbon stream to lower boiling hydrocarbons.

The hydrocracking reactor 36 may comprise one or more vessels, multiplebeds of catalyst in each vessel, and various combinations ofhydrotreating catalyst and hydrocracking catalyst in one or morevessels. In some aspects, the hydrocracking reaction provides totalconversion of at least about 20 vol-% and typically greater than about60 vol-% of the hydrocarbon feed to products boiling below the dieselcut point. The hydrocracking reactor 36 may operate at partialconversion of more than about 50 vol-% or full conversion of at leastabout 90 vol-% of the feed based on total conversion. To maximizediesel, full conversion is effective. The first vessel or bed mayinclude hydrotreating catalyst for the purpose of demetallizing,desulfurizing or denitrogenating the hydrocracking feed.

The hydrocracking reactor 36 may be operated at mild hydrocrackingconditions. Mild hydrocracking conditions will provide about 20 to about60 vol-%, preferably about 20 to about 50 vol-%, total conversion of thehydrocarbon feed to product boiling below the diesel cut point. In mildhydrocracking, converted products are biased in favor of diesel. In amild hydrocracking operation, the hydrotreating catalyst has just asmuch or a greater conversion role than hydrocracking catalyst.Conversion across the hydrotreating catalyst may be a significantportion of the overall conversion. If the hydrocracking reactor 36 isintended for mild hydrocracking, it is contemplated that the mildhydrocracking reactor 36 may be loaded with all hydrotreating catalyst,all hydrocracking catalyst, or some beds of hydrotreating catalyst andbeds of hydrocracking catalyst. In the last case, the beds ofhydrocracking catalyst may typically follow beds of hydrotreatingcatalyst. Most typically, three beds of hydrotreating catalyst may befollowed by zero, one or two 2 beds of hydrocracking catalyst.

The hydrocracking reactor 36 in FIG. 1 has four beds in one reactorvessel. If mild hydrocracking is desired, it is contemplated that thefirst three catalyst beds comprise hydrotreating catalyst and the lastcatalyst bed comprise hydrocracking catalyst. If partial or fullhydrocracking is preferred, additional beds of hydrocracking catalystmay be used than in mild hydrocracking.

At mild hydrocracking conditions, the feed is selectively converted toheavy products such as diesel and kerosene with a low yield of lighterhydrocarbons such as naphtha and gas. Pressure is also moderate to limitthe hydrogenation of the bottoms product to an optimal level fordownstream processing.

In one aspect, for example, when a balance of middle distillate andgasoline is preferred in the converted product, mild hydrocracking maybe performed in the first hydrocracking reactor 36 with hydrocrackingcatalysts that utilize amorphous silica-alumina bases or low-levelzeolite bases combined with one or more Group VIII or Group VIB metalhydrogenating components. In another aspect, when middle distillate issignificantly preferred in the converted product over gasolineproduction, partial or full hydrocracking may be performed in the firsthydrocracking reactor 36 with a catalyst which comprises, in general,any crystalline zeolite cracking base upon which is deposited a GroupVIII metal hydrogenating component. Additional hydrogenating componentsmay be selected from Group VIB for incorporation with the zeolite base.

The zeolite cracking bases are sometimes referred to in the art asmolecular sieves and are usually composed of silica, alumina and one ormore exchangeable cations such as sodium, magnesium, calcium, rare earthmetals, etc. They are further characterized by crystal pores ofrelatively uniform diameter between about 4 and about 14 Angstroms(10⁻¹⁰ meters). It is preferred to employ zeolites having a relativelyhigh silica/alumina mole ratio between about 3 and about 12. Suitablezeolites found in nature include, for example, mordenite, stilbite,heulandite, ferrierite, dachiardite, chabazite, erionite and faujasite.Suitable synthetic zeolites include, for example, the B, X, Y and Lcrystal types, e.g., synthetic faujasite and mordenite. The preferredzeolites are those having crystal pore diameters between about 8-12Angstroms (10⁻¹⁰ meters), wherein the silica/alumina mole ratio is about4 to 6. One example of a zeolite falling in the preferred group issynthetic Y molecular sieve.

The natural occurring zeolites are normally found in a sodium form, analkaline earth metal form, or mixed forms. The synthetic zeolites arenearly always prepared first in the sodium form. In any case, for use asa cracking base it is preferred that most or all of the originalzeolitic monovalent metals be ion-exchanged with a polyvalent metaland/or with an ammonium salt followed by heating to decompose theammonium ions associated with the zeolite, leaving in their placehydrogen ions and/or exchange sites which have actually beendecationized by further removal of water. Hydrogen or “decationized” Yzeolites of this nature are more particularly described in U.S. Pat. No.3,130,006.

Mixed polyvalent metal-hydrogen zeolites may be prepared byion-exchanging first with an ammonium salt, then partially backexchanging with a polyvalent metal salt and then calcining. In somecases, as in the case of synthetic mordenite, the hydrogen forms can beprepared by direct acid treatment of the alkali metal zeolites. In oneaspect, the preferred cracking bases are those which are at least about10 percent, and preferably at least about 20 percent,metal-cation-deficient, based on the initial ion-exchange capacity. Inanother aspect, a desirable and stable class of zeolites is one whereinat least about 20 percent of the ion exchange capacity is satisfied byhydrogen ions.

The active metals employed in the preferred hydrocracking catalysts ofthe present invention as hydrogenation components are those of GroupVIII, i.e., iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium,iridium and platinum. In addition to these metals, other promoters mayalso be employed in conjunction therewith, including the metals of GroupVIB, e.g., molybdenum and tungsten. The amount of hydrogenating metal inthe catalyst can vary within wide ranges. Broadly speaking, any amountbetween about 0.05 percent and about 30 percent by weight may be used.In the case of the noble metals, it is normally preferred to use about0.05 to about 2 wt-%.

The method for incorporating the hydrogenating metal is to contact thebase material with an aqueous solution of a suitable compound of thedesired metal wherein the metal is present in a cationic form. Followingaddition of the selected hydrogenating metal or metals, the resultingcatalyst powder is then filtered, dried, pelleted with added lubricants,binders or the like if desired, and calcined in air at temperatures of,e.g., about 371° to about 648° C. (about 700° to about 1200° F.) inorder to activate the catalyst and decompose ammonium ions.Alternatively, the base component may first be pelleted, followed by theaddition of the hydrogenating component and activation by calcining.

The foregoing catalysts may be employed in undiluted form, or thepowdered catalyst may be mixed and copelleted with other relatively lessactive catalysts, diluents or binders such as alumina, silica gel,silica-alumina cogels, activated clays and the like in proportionsranging between about 5 and about 90 wt-%. These diluents may beemployed as such or they may contain a minor proportion of an addedhydrogenating metal such as a Group VIB and/or Group VIII metal.Additional metal promoted hydrocracking catalysts may also be utilizedin the process of the present invention which comprises, for example,aluminophosphate molecular sieves, crystalline chromosilicates and othercrystalline silicates. Crystalline chromosilicates are more fullydescribed in U.S. Pat. No. 4,363,718.

By one approach, the hydrocracking conditions may include a temperaturefrom about 290° C. (550° F.) to about 468° C. (875° F.), preferably 343°C. (650° F.) to about 435° C. (815° F.), a pressure from about 3.5 MPa(500 psig) to about 20.7 MPa (3000 psig), a liquid hourly space velocity(LHSV) from about 1.0 to less than about 2.5 hr⁻¹ and a hydrogen rate ofabout 421 to about 2,527 Nm³/m³ oil (2,500-15,000 scf/bbl). If mildhydrocracking is desired, conditions may include a temperature fromabout 315° C. (600° F.) to about 441° C. (825° F.), a pressure fromabout 5.5 to about 13.8 MPa (gauge) (800 to 2000 psig) or more typicallyabout 6.9 to about 11.0 MPa (gauge) (1000 to 1600 psig), a liquid hourlyspace velocity (LHSV) from about 0.5 to about 2 hr⁻¹ and preferablyabout 0.7 to about 1.5 hr⁻¹ and a hydrogen rate of about 421 to about1,685 Nm³/m³ oil (2,500-10,000 scf/bbl).

A hydrocracking effluent exits the hydrocracking reactor 36 in line 38.The hydrocracking effluent in line 38 is heat exchanged with thehydrocracking feed in line 34 and in an embodiment may be cooled beforeentering a cold separator 40. The cold separator 40 is in downstreamcommunication with the hydrocracking reactor 36. The cold separator maybe operated at about 46° to about 63° C. (115° to 145° F.) and justbelow the pressure of the hydrocracking reactor 36 accounting forpressure drop to keep hydrogen and light gases in the overhead andnormally liquid hydrocarbons in the bottoms. The cold separator 40provides the vaporous hydrocracking effluent stream comprising hydrogenin an cold separator overhead line 42 and a liquid hydrocrackingeffluent stream in a cold separator bottoms line 44. The cold separatoralso has a boot for collecting an aqueous phase in line 46. The vaporoushydrocracking effluent stream in the overhead line 42 may be scrubbedwith a solution to remove ammonia and hydrogen sulfide as isconventional prior to recycle of the vaporous hydrocracking effluentstream comprising hydrogen to the recycle gas compressor 50.

At least a portion of the hydrocracking effluent stream 38 may befractionated in a fractionation section 16 in downstream communicationwith the hydrocracking reactor 36 to produce a diesel stream in line 86.In an aspect, the liquid hydrocracking effluent stream 44 may befractionated in the fractionation section 16. In a further aspect, thefractionation section 16 may include a cold flash drum 48. The liquidhydrocracking effluent stream 44 may be flashed in the cold flash drum48 which may be operated at the same temperature as the cold separator40 but at a lower pressure of between about 1.4 MPa and about 3.1 MPa(gauge) (200-450 psig) to provide a light liquid stream in a bottomsline 62 from the liquid hydrocracking effluent stream and a light endsstream in an overhead line 64. The aqueous stream in line 46 from theboot of the cold separator may also be directed to the cold flash drum48. A flash aqueous stream is removed from a boot in the cold flash drum48 in line 66. The light liquid stream in bottoms line 62 may be furtherfractionated in the fractionation section 16.

The fractionation section 16 may include a stripping column 70 and afractionation column 80. The light liquid stream in bottoms line 62 maybe heated and fed to the stripping column 70. The light liquid streamwhich is liquid hydrocracking effluent may be stripped with steam fromline 72 to provide a light ends stream of hydrogen, hydrogen sulfide,steam and other gases in an overhead line 74. A portion of the lightends stream may be condensed and refluxed to the stripper column 70. Thestripping column 70 may be operated with a bottoms temperature betweenabout 232° and about 288° C. (450° to 550° F.) and an overhead pressureof about 690 to about 1034 kPa (gauge) (100 to 150 psig). A hydrocrackedbottoms stream in line 76 may be heated in a fired heater and fed to thefractionation column 80.

The fractionation column 80 may also strip the hydrocracked bottoms withsteam from line 82 to provide an overhead naphtha stream in line 84, adiesel stream in line 86 from a side cut and an unconverted oil streamin line 88 which may be suitable for further processing, such as in anFCC unit. The overhead naphtha stream in line 84 may require furtherprocessing before blending in the gasoline pool. It will usually requirecatalytic reforming to improve the octane number. The reforming catalystwill often require the overhead naphtha to be further desulfurized in anaphtha hydrotreater prior to reforming. In an aspect, the hydrocrackednaphtha may be desulfurized in an integrated hydrotreater 92. It is alsocontemplated that a further side cut be taken to provide a separatelight diesel or kerosene stream taken above a heavy diesel stream takenin line 86. A portion of the overhead naphtha stream in line 84 may becondensed and refluxed to the fractionation column 80. The fractionationcolumn 80 may be operated with a bottoms temperature between about 288°and about 385° C. (550° to 725° F.), preferably between about 315° andabout 357° C. (600° to 675° F.) and at or near atmospheric pressure. Aportion of the hydrocracked bottoms may be reboiled and returned to thefractionation column 80 instead of using steam stripping.

The diesel stream in line 86 is reduced in sulfur content but may notmeet a low sulfur diesel (LSD) specification which is less than 50 wppmsulfur, an ULSD specification which is less than 10 wppm sulfur, orother specifications. Hence, it must be further finished in the dieselhydrotreating unit 14.

The diesel stream in line 86 may be joined by the second hydrotreatinghydrogen stream taken from the compressed hydrogen stream in thecompressed hydrogen line 52 at the split 54 in a second hydrogen splitline 56 to provide a hydrotreating feed stream 90. The diesel stream inline 86 may also be mixed with a co-feed that is not shown. Thehydrotreating feed stream 90 may be heat exchanged with thehydrotreating effluent in line 94, further heated in a fired heater anddirected to a hydrotreating reactor 92. Consequently, the hydrotreatingreactor is in downstream communication with the fractionation section16, the compressed hydrogen line 52 and the hydrocracking reactor 36. Inthe hydrotreating reactor 92, the diesel stream is hydrotreated in thepresence of a hydrotreating hydrogen stream and hydrotreating catalystto provide a hydrotreating effluent stream 94. In an aspect, all of thehydrotreating hydrogen stream is provided from the compressed hydrogenstream in line 52 via second hydrogen split line 56.

The hydrotreating reactor 92 may comprise more than one vessel andmultiple beds of catalyst. The hydrotreating reactor 92 in FIG. 1 hastwo beds in one reactor vessel. In the hydrotreating reactor,hydrocarbons with heteroatoms are further demetallized, desulfurized anddenitrogenated. The hydrotreating reactor may also contain hydrotreatingcatalyst that is suited for saturating aromatics, hydrodewaxing andhydroisomerization.

If the hydrocracking reactor 36 is operated as a mild hydrocrackingreactor, the hydrocracking reactor may operate to convert up to about20-60 vol-% of feed boiling above diesel boiling range to productboiling in the diesel boiling range. Consequently, the hydrotreatingreactor 92 should have very low conversion and is primarily fordesulfurization if integrated with a mild hydrocracking reactor 36 tomeet fuel specifications such as qualifying as ULSD.

Hydrotreating is a process wherein hydrogen gas is contacted withhydrocarbon in the presence of suitable catalysts which are primarilyactive for the removal of heteroatoms, such as sulfur, nitrogen andmetals from the hydrocarbon feedstock. In hydrotreating, hydrocarbonswith double and triple bonds may be saturated. Aromatics may also besaturated. Some hydrotreating processes are specifically designed tosaturate aromatics. Cloud point of the hydrotreated product may also bereduced. Suitable hydrotreating catalysts for use in the presentinvention are any known conventional hydrotreating catalysts and includethose which are comprised of at least one Group VIII metal, preferablyiron, cobalt and nickel, more preferably cobalt and/or nickel and atleast one Group VI metal, preferably molybdenum and tungsten, on a highsurface area support material, preferably alumina. Other suitablehydrotreating catalysts include zeolitic catalysts, as well as noblemetal catalysts where the noble metal is selected from palladium andplatinum. It is within the scope of the present invention that more thanone type of hydrotreating catalyst be used in the same hydrotreatingreactor 92. The Group VIII metal is typically present in an amountranging from about 2 to about 20 wt-%, preferably from about 4 to about12 wt-%. The Group VI metal will typically be present in an amountranging from about 1 to about 25 wt-%, preferably from about 2 to about25 wt-%.

Preferred hydrotreating reaction conditions include a temperature fromabout 290° C. (550° F.) to about 455° C. (850° F.), suitably 316° C.(600° F.) to about 427° C. (800° F.) and preferably 343° C. (650° F.) toabout 399° C. (750° F.), a pressure from about 4.1 MPa (600 psig),preferably 6.2 MPa (900 psig) to about 13.1 MPa (1900 psig), a liquidhourly space velocity of the fresh hydrocarbonaceous feedstock fromabout 0.5 hr⁻¹ to about 4 hr⁻¹, preferably from about 1.5 to about 3.5hr⁻¹, and a hydrogen rate of about 168 to about 1,011 Nm³/m³ oil(1,000-6,000 scf/bbl), preferably about 168 to about 674 Nm³/m³ oil(1,000-4,000 scf/bbl) for diesel feed, with a hydrotreating catalyst ora combination of hydrotreating catalysts. The hydrotreating unit 14 isintegrated with the hydrocracking unit 12, so they both operate at aboutthe same pressure accounting for normal pressure drop.

The hydrotreating effluent stream in line 94 may be heat exchanged withthe hydrotreating feed stream in line 90. The hydrotreating effluentstream in line 94 may be separated in a warm separator 96 to provide avaporous hydrotreating effluent stream comprising hydrogen in a warmseparator overhead line 98 and a liquid hydrotreating effluent stream ina warm separator bottoms line 100. The vaporous hydrotreating effluentstream comprising hydrogen may be mixed with the hydrocracking effluentstream in line 38 perhaps prior to cooling and enter into the coldseparator 40. The warm separator 96 may be operated between about 149°and about 260° C. (300° to 500° F.). The pressure of the warm separator96 is just below the pressure of the hydrotreating reactor 96 accountingfor pressure drop. The warm separator may be operated to obtain at least90 wt-% diesel and preferably at least 93 wt-% diesel in the liquidstream in line 100. All of the other hydrocarbons and gases go up in thevaporous hydrotreating effluent stream in line 98 which joins thehydrocracking effluent in line 38 and may be processed after heatingtherewith first by entering the cold separator 40. Consequently, thecold separator 40 and, thereby, the recycle gas compressor 50 are indownstream communication with the warm separator overhead line 98.Accordingly, recycle gas loops from both the hydrocracking section 12and the hydrotreating section 14 share the same recycle gas compressor50. Moreover, at least a portion of the hydrotreating effluent stream inhydrotreating effluent line 94 provided in the warm separator overheadstream comprising hydrogen and hydrocarbons lighter than diesel in thewarm separator overhead line 98 is mixed with at least a portion of thehydrocracking effluent stream in hydrocracking effluent line 38.

The liquid hydrotreating effluent stream in line 100 may be fractionatedin a hydrotreating stripper column 102. In an aspect, fractionation ofthe liquid hydrotreating effluent stream in line 100 may includeflashing it in a warm flash drum 104 which may be operated at the sametemperature as the warm separator 96 but at a lower pressure of betweenabout 1.4 MPa and about 3.1 MPa (gauge) (200-450 psig). A warm flashoverhead stream in the warm flash overhead line 106 may be joined to theliquid hydrocracking effluent stream in the cold separator bottoms line44 for further fractionation therewith. Consequently, at least a portionof the hydrotreating effluent stream in line 94 comprising hydrogenprovided in the warm flash overhead stream in the warm flash overheadline 106 is mixed with at least a portion of the hydrocracking effluentstream in line 38 provided in the liquid hydrocracking effluent streamin the cold separator bottoms line 44.

The warm flash bottoms stream in line 108 may be heated and fed to thestripper column 102. The warm flash bottoms may be stripped in thestripper column 102 with steam from line 110 to provide a naphtha andlight ends stream in overhead line 112. The naphtha and light endsstream in line 112 may be fed to the fractionation section 16 andspecifically to the stripping column 70 at an elevation above the feedpoint of light liquid stream in line 62. A product diesel stream isrecovered in bottoms line 114 comprising less than 50 wppm sulfurqualifying it as LSD and preferably less than 10 wppm sulfur qualifyingit as ULSD. It is contemplated that the stripper column 102 may beoperated as a fractionation column with a reboiler instead of withstripping steam.

By operating the warm separator 96 at elevated temperature to rejectmost hydrocarbons lighter than diesel, the hydrotreating strippingcolumn 102 may be operated more simply because it is not relied upon toseparate naphtha from lighter components and because there is verylittle naphtha to separate from the diesel. Moreover, the warm separator96 makes sharing of a cold separator 40 with the hydrocracking reactor36 possible and heat useful for fractionation in the stripper column 102is retained in the hydrotreating liquid effluent.

FIG. 2 illustrates an embodiment of a process and apparatus 8′ thatutilizes a hot separator 120 to initially separate the hydrocrackingeffluent in line 38′. Many of the elements in FIG. 2 have the sameconfiguration as in FIG. 1 and bear the same reference number. Elementsin FIG. 2 that correspond to elements in FIG. 1 but have a differentconfiguration bear the same reference numeral as in FIG. 1 but aremarked with a prime symbol (′).

The hot separator 120 in the hydrocracking section 12′ is in downstreamcommunication with the hydrocracking reactor 36 and provides a vaporoushydrocarbonaceous stream in an overhead line 122 and a liquidhydrocarbonaceous stream in a bottoms line 124. The hot separator 120operates at about 177° to about 343° C. (350° to 650° F.) and preferablyoperates at about 232° to about 288° C. (450° to 550° F.). The hotseparator may be operated at a slightly lower pressure than thehydrocracking reactor 36 accounting for pressure drop. The vaporoushydrocarbonaceous stream in line 122 may be joined by the vaporoushydrotreating effluent stream in line 98′ from the hydrotreating section14′ and be mixed and transported together in line 126. The mixed streamin line 126 may be cooled before entering the cold separator 40.Consequently, the vaporous hydrocracking effluent may be separated alongwith the vaporous hydrotreating effluent stream in the cold separator 40to provide the vaporous hydrocracking effluent comprising hydrogen inline 42 and the liquid hydrocracking effluent in line 44 and which areprocessed as previously described with respect to FIG. 1. The coldseparator 40, therefore, is in downstream communication with theoverhead line 122 of the hot separator 120 and an overhead line 98′ ofthe warm separator 96.

The liquid hydrocarbonaceous stream in bottoms line 124 may befractionated in the fractionation section 16′. In an aspect, the liquidhydrocarbonaceous stream in line 124 may be flashed in a hot flash drum130 to provide a light ends stream in an overhead line 132 and a heavyliquid stream in a bottoms line 134. The hot flash drum 130 may beoperated at the same temperature as the hot separator 120 but at a lowerpressure of between about 1.4 MPa and about 3.1 MPa (gauge) (200 to 450psig). The heavy liquid stream in bottoms line 134 may be furtherfractionated in the fractionation section 16′. In an aspect, the heavyliquid stream in line 134 may be introduced into the stripping column 70at a lower elevation than the feed point light liquid stream in line 62.

The rest of the embodiment in FIG. 2 may be the same as described forFIG. 1 with the previous noted exceptions.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention. Itshould be understood that the illustrated embodiments are exemplaryonly, and should not be taken as limiting the scope of the invention.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing, all temperatures are set forth in degrees Celsius and,all parts and percentages are by weight, unless otherwise indicated.Pressures are given at the vessel outlet and particularly at the vaporoutlet in vessels with multiple outlets.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. An apparatus for producing diesel comprising: a hydrocracking reactorin communication with a compressor on a make-up hydrogen line and ahydrocarbon feed line for hydrocracking the hydrocarbon stream to lowerboiling hydrocarbons; a recycle gas compressor in communication with thehydrocracking reactor and the make-up hydrogen line for compressing avaporous hydrocracking effluent stream comprising hydrogen and acompressed make-up hydrogen stream to provide a compressed hydrogenstream in a compressed hydrogen line; and a hydrotreating reactor incommunication with the compressed hydrogen line and the hydrocrackingreactor for hydrotreating a diesel stream to produce low sulfur diesel.2. The apparatus of claim 1 further comprising a fractionation sectionin communication with the hydrocracking reactor for fractionating ahydrocracking effluent stream to produce the diesel stream and thehydrotreating reactor being in communication with the fractionationsection.
 3. The apparatus of claim 1 further comprising a split on thecompressed hydrogen line providing a first hydrogen split line incommunication with the hydrocracking reactor and a second hydrogen splitline in communication with the hydrotreating reactor.
 4. The apparatusof claim 3 wherein the recycle gas compressor is in downstreamcommunication with a compressed make-up hydrogen line.
 5. The apparatusof claim 1 further comprising a warm separator in communication with thehydrotreating reactor for separating the hydrotreating effluent streaminto a vaporous hydrotreating effluent stream comprising hydrogen in anoverhead line and a liquid hydrotreating effluent stream in a bottomsline and the recycle gas compressor in communication with the overheadline.
 6. The apparatus of claim 5 further comprising a cold separator incommunication with the hydrocracking reactor for providing the vaporoushydrocracking effluent stream comprising hydrogen in an overhead lineand the liquid hydrocracking effluent stream in a bottoms line and thecold separator being in communication with an overhead line of the warmseparator.
 7. The apparatus of claim 6 further comprising a hotseparator in communication with the hydrocracking reactor for providinga vaporous hydrocarbonaceous stream in an overhead line and a liquidhydrocarbonaceous stream in a bottoms line and the cold separator incommunication with the overhead line of the hot separator and anoverhead line of the warm separator.
 8. The apparatus of claim 5 furthercomprising a fractionation column in communication with the bottoms lineof the warm separator for fractionating the liquid hydrotreatingeffluent stream to provide a low sulfur diesel stream.
 9. An apparatusfor producing diesel comprising: a make-up hydrogen stream; one or morecompressors in communication with the make-up hydrogen line forcompressing the make-up hydrogen stream; a hydrocarbon feed line forcarrying a hydrocarbon stream; a hydrocracking reactor in communicationwith the make-up hydrogen line and the hydrocarbon feed line forhydrocracking the hydrocarbon stream to lower boiling hydrocarbons; arecycle gas compressor in communication with the hydrocracking reactorand the one or more compressors for compressing a vaporous hydrocrackingeffluent stream comprising hydrogen and a compressed make-up hydrogenstream to provide a compressed hydrogen stream in a compressed hydrogenline; a fractionation section in communication with the hydrocrackingreactor for fractionating a liquid hydrocracking effluent stream toproduce a diesel stream carried in a diesel line; and a hydrotreatingreactor in communication with the compressed hydrogen line and thediesel line for hydrotreating the diesel stream to produce low sulfurdiesel.
 10. The apparatus of claim 9 further comprising a split on thecompressed hydrogen line providing a first hydrogen split line incommunication with the hydrocracking reactor and a second hydrogen splitline in communication with the hydrotreating reactor.
 11. The apparatusof claim 10 wherein the recycle gas compressor is in downstreamcommunication with a compressed make-up hydrogen line.
 12. The apparatusof claim 9 further comprising a warm separator in communication with thehydrotreating reactor for separating the hydrotreating effluent streaminto a vaporous hydrotreating effluent stream comprising hydrogen in anoverhead line and a liquid hydrotreating effluent stream in a bottomsline and the recycle gas compressor in communication with the overheadline.
 13. The apparatus of claim 12 further comprising a cold separatorin communication with the hydrocracking reactor for providing thevaporous hydrocracking effluent stream comprising hydrogen in anoverhead line and the liquid hydrocracking effluent stream in a bottomsline and the cold separator being in communication with an overhead lineof the warm separator.
 14. The apparatus of claim 13 further comprisinga hot separator in communication with the hydrocracking reactor forproviding a vaporous hydrocarbonaceous stream in an overhead line and aliquid hydrocarbonaceous stream in a bottoms line and the cold separatorin communication with the overhead line of the hot separator and anoverhead line of the warm separator.
 15. The apparatus of claim 13further comprising the fractionation section in communication with thebottoms line of the cold separator.
 16. The apparatus of claim 12further comprising a fractionation column in communication with thebottoms line of the warm separator for fractionating the liquidhydrotreating effluent stream to provide a low sulfur diesel stream. 17.The apparatus of claim 12 further comprising a fractionation column incommunication with the hydrotreating reactor for fractionating ahydrotreating effluent stream to provide a low sulfur diesel stream. 18.An apparatus for producing diesel comprising: a hydrocracking reactor incommunication with one or more compressors on a make-up hydrogen lineand a hydrocarbon feed line for hydrocracking the hydrocarbon stream tolower boiling hydrocarbons; a recycle gas compressor in communicationwith the make-up hydrogen line and the hydrocracking reactor forcompressing a vaporous hydrocracking effluent stream comprising hydrogento provide a compressed hydrogen stream in a compressed hydrogen line; ahydrotreating reactor in communication with the compressed hydrogen lineand the hydrocracking reactor for hydrotreating the diesel stream toproduce low sulfur diesel; and a warm separator in communication withthe hydrotreating reactor for separating the hydrotreating effluentstream into a vaporous hydrotreating effluent stream comprising hydrogenin an overhead line and a liquid hydrotreating effluent stream in abottoms line and the recycle gas compressor in communication with theoverhead line.
 19. The apparatus of claim 18 further comprising afractionation section in communication with the hydrocracking reactorfor fractionating a hydrocracking effluent stream to produce a dieselstream and the hydrotreating reactor being in communication with thefractionation section.
 20. The apparatus of claim 18 further comprisinga cold separator in communication with the hydrocracking reactor forproviding the vaporous hydrocracking effluent stream comprising hydrogenin an overhead line and the liquid hydrocracking effluent stream in abottoms line and the cold separator being in communication with anoverhead line of the warm separator.